The invention relates to a method of adjusting the radio frequency of a repeater in a cellular radio network, the repeater amplifying radio signals of a bi-directional radio connection between a base station and a subscriber terminal at least at one particular radio frequency.
Cellular radio networks use repeaters for covering shadow regions of a base station. The shadow regions are caused by difficult terrain conditions, including mountains, buildings and tunnels. The repeater advantageously improves the quality of a radio connection between the base station and the subscriber terminal, since the acquisition and operating costs of the repeater, being simpler in structure, are lower than those of the actual base station. The repeater, as compared with the base station, provides a considerable saving particularly in telecommunication connections, because it does not need expensive fixed transmission capacity which is required between the base station and a base station controller.
The repeaters are most commonly used in road tunnels, underground stations, car parks and other similar locations under ground from where it is difficult or impossible to implement a direct radio connection to the base station. The use of the repeaters is more difficult in an open terrain, because a radio signal propagates over two paths between the base station and the subscriber terminal: directly and via the repeater. This brings about interference in the form of multipath-propagated signal components to the received signal.
The repeater thus amplifies the signals of a base station that operates at a particular frequency. Each repeater must be adjusted to amplify radio frequencies used by a particular base station. When a large number of repeaters is involved, adjusting them to the correct frequency becomes a laborious task that is prone to errors. Typically, a network administrator must perform frequency changes in the network in connection with the extension, increase of capacity and tuning of the network. When frequencies are reallocated, the repeaters within the area of each base station must also be modified to use the radio frequencies in accordance with a new frequency plan, for the repeaters are channel selective and must therefore be configured to use the desired frequencies. Broadband repeaters which do not need to be tuned to the desired frequency are also known in the field.
In the prior art, the repeaters are manually adjusted to use the desired frequencies. In that case, a person in charge of maintenance travels to each repeater and adjusts, either mechanically or via a computer that is connected to the serial port of the repeater, the frequencies used by the repeater. In another approach, the person in charge of maintenance adjusts the frequencies by manual remote control. In that case, the repeater is arranged to receive information on the correct frequency by a radio modem, for example. The radio modem may be a conventional GSM telephone, for example, with a modem card connected thereto. The repeater may also be arranged to receive information on the correct frequencies via a shortmessage service, in which case a GSM telephone is also connected to the repeater.
However, a problem in the above-mentioned arrangements is that they are manual operations involving extra work and being also extremely prone to errors.
An object of the invention is thus to provide a method and equipment implementing the method so as to solve the above-mentioned problems. This is achieved by the method of the type presented in the introduction, which is characterized in that the repeater monitors the radio signals transmitted by at least one base station and automatically tunes to amplify the signals of the particular radio frequency on the basis of the information included in the radio signals it has monitored.
The invention also relates to a repeater in a cellular radio network, amplifying radio signals of a bi-directional radio connection between a base station and a subscriber terminal at least at one particular radio frequency.
The repeater of the invention is characterized in that the repeater comprises monitoring means for monitoring the radio signals transmitted by at least one base station, and adjustment means for automatically tuning to amplify the radio signals of a particular radio frequency on the basis of the information included in the radio signals it has monitored.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea that no special measures need be taken in order to change the frequencies amplified by a repeater. The repeater monitors information that is even normally transmitted by a base station, and concludes the frequency at which it should operate on the basis of the information.
The method and system of the invention provide many advantages. A person in charge of maintenance does not need to take any measures in order to set the frequencies used by the repeater. The work contribution previously required in order to accomplish the task is no longer needed. In addition, the risk of committing errors becomes considerably smaller. As compared with the prior art manual remote control, the solution of the invention does not involve extra costs.